Freshwater Copepods

What are Freshwater Copepods?

Freshwater Copepods belong to the Crustacea classification and look much like tiny one-eyed lobsters, measuring between 0.5 mm to 2.0 mm in length. These creatures represent a type of zooplankton found in numerous freshwater ecosystems, though they can also thrive in saltwater environments. Copepods display a diverse range in terms of species and dietary habits. Many act as filterers, collectors, or predators, mainly consuming algae, bacteria, and small detritus particles. Meanwhile, some of the larger species take on a predatory role, actively hunting smaller zooplankton like the soft-bodied rotifers.


Copepods vary in size and shape, but you can typically identify them easily, though pinpointing the exact species might be trickier. They often feature a bullet-shaped body, protruding antennae, and a distinct (usually red) eyespot at the centre of their head. The body segments into a head — which often fuses with the first thoracic segment — and an abdomen that ends in two spiny tails known as caudal rami. Female copepods sometimes carry egg sacks above these tails. One way to recognize copepods is by their unique, rapid flicking movement in the water, which they perform in short, swift bursts.


You’ll find copepods in almost every healthy body of water, ranging from ponds, lakes, and rivers to marshes.

Role in the Ecosystem

Copepods serve a crucial function in aquatic food webs. They act as primary and secondary consumers and are a staple food source for many larger invertebrates and fish species, including fish fry. By bridging the gap between primary producers and top-tier predators and with their 13 life stages, they offer a variety of sizes catering to different predators. Additionally, copepods contribute significantly to water quality by filtering debris and aiding in matter decomposition.

Benefits in an Aquarium

Adding copepods enhances your Aquarium’s biodiversity and overall health. These creatures help clean the water by consuming decaying plant matter and serve as a nutritious, live food source for smaller fish and fry. Once they’re established, cultivating freshwater copepods becomes straightforward, making them a valuable addition to any tank ecosystem. For those who breed fish, copepods present a superior, protein-rich alternative to brine shrimp, boosting young fish’s health and growth rates.


  • Brandl, Z. (2005). Freshwater Copepods and Rotifers: Predators and their Prey. Hydrobiologia, 546, 475–489.
  • Kwok, W.H., Souissi, S., & Dur, G. (2015). Aquatic Ecotoxicology. 1st ed. Elsevier Inc.
  • Hamrsky, J. (2019). Freshwater copepods (Copepoda). LIFE IN FRESHWATER. Available online [Accessed 18 Feb. 2020]
  • Thorp, J.H., & Covich, A.P. (2019). Thorp and Covich’s Freshwater Invertebrates: Volume 4: Keys to Palaearctic Fauna. [Accessed 18 Feb. 2020]
  • Thorp, J.H., & Covich, A.P. (2009). Ecology and Classification of North American Freshwater Invertebrates (3rd Edition). [Accessed 18 Feb. 2020]